This invention relates to a seal device for use in a tire pressure-adjusting device for adjusting the pressure of a tire of an automobile from the driver's seat.
The inflation pressure of a tire of an automobile greatly influences not only safety, such as the braking and the steering, but also the life of the tire and the ride of the automobile. For this reason, recently, there has been developed a tire pressure-adjusting device for properly adjusting the tire pressure in accordance with the running condition from the room of the automobile.
In a conventional tire pressure-adjusting device, compressed air is supplied from an air supply source via an air pipe to an air passage in an axle case, and the compressed air is further fed from this air passage into the tire via an air passage, formed in the axle, and an air pipe. The axle case is not rotatable, and the axle is rotatable, and therefore in the supply of the air via the air passages, it is of absolute necessity to provide a seal device at the area of relative rotation between the axle case and the axle.
One such conventional seal device is disclosed, for example, in Japanese Utility Model Unexamined Publication No. 62-151104. As shown in FIG. 6, in this seal device, a seal-mounting portion 2 is formed in an inner surface of an axle case 1, and a pair of pressure-resistant oil seals 6 and 7 are provided at the seal-mounting portion 2 in opposed relation to each other, with a spacer 5 interposed between the oil seals 6 and 7. The spacer 5 has an air hole 4 in communication with an air hole 3 formed in the axle case 1. The oil seals 6 and 7 are fixed relative to the axle case 1 by a retainer ring 8. Distal ends 6a and 7a of lips of the oil seals 6 and 7 are pressed against an outer peripheral surface of an axle 9, and an air passage 10 formed in the axle 9 is open at one end to that portion of the outer peripheral surface of the axle 9 lying between the lip ends 6a and 7a. Therefore, compressed air supplied in a direction indicated by arrow A passes through the air hole 3 of the axle case 1 and the air hole 4 of the spacer 5, and is introduced into a closed or sealed space defined by the pair of oil seals 6 and 7, the spacer 5 and the axle 9. The compressed air is further fed from this sealed space to a tire via the air passage 10 of the axle 9 in a direction indicated by arrow B.
Each of the lip ends 6a and 7a of the oil seals 6 and 7 is in line-contact with the outer peripheral surface of the axle 9, and therefore this contact pressure is increased when supplying the compressed air, so that wear of the lip ends 6a and 7a is promoted. This results in a problem that the sealing properties of the seal device can not be maintained properly over a prolonged period of time. In addition, since the space defined by the pair of oil seals 6 and 7, the spacer 5 and the axle 9 is always in communication with the air holes 3 and 4 and the air passage 10, grease can not be sealed in this space. Thus, the only object to be sealed is the air, and therefore the air is liable to leakage, and besides because of inadequate lubrication, the lip ends 6a and 7a are subjected to premature wear, which also results in failure to properly maintain the sealing properties over a long period of time.